Transcription of DNA to RNA

Transcription of DNA to RNA

Overview

• Transcription is the first step in gene expression.
• It involves the production of a complementary RNA molecule from a DNA template.

Stage 1: Initiation

• Transcription starts at a specific location in the DNA called the promoter.
• An enzyme called RNA polymerase binds to the promoter.
• The DNA double helix unwinds, exposing the template strand that will guide RNA synthesis.

Stage 2: Elongation

• RNA polymerase uses nucleotide triphosphates as substrates to replicate the DNA sequence.
• It synthesises the new RNA strand in the 5’ to 3’ direction.
• The DNA that has been transcribed rewinds into a double helix.

Stage 3: Termination

• Once a gene is completely transcribed, the process of transcription ends.
• The RNA transcript, a mirrored copy of the original DNA sequence, is complete.
• The RNA molecule then detaches from the DNA.

Post-Transcription Modification in Eukaryotes

• This process only occurs in eukaryotic cells.
• Newly transcribed RNA, known as primary transcript or pre-mRNA, undergoes modification to become mRNA.
• A 5’ cap and a poly-A tail are added for protection and transport out of the nucleus.
• Introns are non-coding sequences that are removed, while exons, the coding sequences, are spliced together.

Significance

• Transcription enables the cell to produce the specific proteins it needs to function.
• Variations in the transcription process can lead to gene expression changes, which can affect an organism’s characteristics.